Recent Accounting Pronouncements - Additional Information (Detail) - Accounting Standards Update 201609 [Member] - USD ($) $ in Millions		12 Months Ended
	Oct. 01, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Reclassification of Excess Tax Benefit from Share-Based Compensation Awards from Cash Flows from Financing to Operating Activities [Member]
Significant Accounting Policies [Line Items]
Reclassification of tax benefit from share-based compensation awards			$ 8	$ 0
(Provision) Benefit for Income Taxes [Member]
Significant Accounting Policies [Line Items]
Discrete tax benefit		$ 2
Maximum [Member]
Significant Accounting Policies [Line Items]
Cumulative-effect of net charge to retained earnings	$ (1)